This present application relates to interior cooling channels and configurations of the blades in gas turbine engines. More specifically, but not by way of limitation, the present application relates to interior cooling channels and configurations formed near the outer radial tip of turbine rotor blades.
It will be appreciated that combustion or gas turbine engines (“gas turbines) include a compressor, combustor, and turbine. The compressor and turbine sections generally include rows of blades that are axially stacked in stages. Each stage includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central turbine axis or shaft. In operation, generally, the compressor rotor blades rotate about the shaft, and, acting in concert with the stator blades, compress a flow of air. The supply of compressed air then is used in the combustor to combust a supply of fuel. The resulting flow of hot expanding gases from the combustion, i.e., the working fluid, is expanded through the turbine section of the engine. The flow of working fluid through the turbine induces the rotor blades to rotate. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated. During operation, because of the extreme temperatures of the hot-gas path, the velocity of the working fluid, and the rotational velocity of the engine, the blades within the turbine become highly stressed with extreme mechanical and thermal loads.
The ever-increasing demand for energy makes the engineering of more efficient gas turbines an ongoing and significant objective. While several strategies for increasing the efficiency of gas turbines are known, it remains a challenging objective because such alternatives—which, for example, include increasing the size of the engine, increasing the temperatures through the hot-gas path, and increasing the rotational velocities of the rotor blades—generally place additional strain on parts that are already highly stressed. As a result, improved apparatus, methods and/or systems that reduce operational stresses placed on turbine blades or allow the turbine blades to better withstand these stresses or operate more efficiently are in great demand.
One strategy for alleviating the thermal stress on the blades is through actively cooling them during operation. Such cooling, for example, may allow the blades to withstand higher firing temperatures, withstand greater mechanical stresses at high operating temperatures, and/or extend the part-life of the blades, all of which may allow the gas turbine to be more cost-effective and efficient in its operation. One way to cool blades during operation is through the use of internal cooling passageways, channels, or circuits. Generally, this involves passing a relatively cool supply of compressed air, which may be supplied by the compressor of the gas turbine, through internal cooling channels within the blades. For a number of reasons, as will be appreciated, great care is required in designing and manufacturing the configuration of these interior cooling channels. First, the use of cooling air comes at a price. That is, air that is diverted from the compressor to the turbine section of the engine for cooling bypasses the combustor and, thus, decreases the efficiency of the engine. Second, newer, more aggressively shaped aerodynamic blade configurations are thinner and more curved or twisted, which requires the cooling channels to perform well while having a compact design. Third, to reduce mechanical loads, cooling channels may be formed to remove unnecessary weight from the blade; however, the blades still must remain strong to withstand extreme mechanical loads. Cooling channels, therefore, must be designed such that the turbine blade is lightweight, yet remains robust, while also limiting stress concentrations and/or effectively cooling those areas where such concentrations are unavoidable. Fourth, cooling configurations may be configured such that coolant exiting the blade enhances efficient operation. Specifically, because coolant exiting from cooling channels disrupts flow through the gas path, it causes aerodynamic loses. Further, the manner in which coolant is released may affect the cooling effect it has once released, i.e., on the outer surface of the blade. Thus, cooling configurations that release coolant so that aerodynamic loses are minimized while cooling effectiveness is enhanced are desirable. Accordingly, cooling configurations that satisfy these several competing criteria in ways that promote structural robustness, component longevity, and efficient usage of coolant are in commercially demand.